Generally, since a secondary battery may be charged and discharged unlike a primary battery, the secondary battery has been applied to various fields such as a digital camera, a cellular phone, a notebook computer, and a hybrid vehicle and has been actively studied. Examples of the secondary battery may include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, a lithium secondary battery, and the like.
Among these secondary batteries, the lithium secondary battery having high energy density and discharging voltage has been mainly studied and has been commercialized and widely used. The lithium secondary battery may be manufactured in various types. As a typical type of the lithium secondary battery, there are a cylinder type and a prismatic type that may be mainly used for a lithium ion battery. A lithium polymer battery that has been recently spotlighted is manufactured in a pouched type having flexibility, such that a shape thereof is relatively free. A plurality of pouched type of battery cells are generally used by connecting with each other to configure a module form. In this case, an electrical connection of each of the battery cells is formed by a connection of an electrode tab protruded to the outside of the battery cell. The module has risks of fire, combustion and explosion due to decay of a molecular structure or internal short-circuit upon overcharging or overdischarging of the secondary battery. For this reason, various methods such as a safety vent, a positive temperature coefficient (PTC), a current interrupt device (CID), and the like are used to secure safety of the battery cell. These methods mainly take advantage of a scheme of minimizing the risks of the fire, the combustion, and the explosion by damaging a predetermined region of the battery cell and decreasing an internal pressure using the damaged predetermined region. However, according to the methods described above, the damaged region of the battery cell is irregularly formed, such that an internal electrolyte may be leaked to the outside through the damaged region.